[dynamo] Add astunparse dependency (#102120)
Summary:
https://github.com/pytorch/pytorch/pull/98488 implements CSE for dynamo guards, and it relies on astunparse to perform the optimization.
`test_guards_cse_pass_single` was broken and later was fixed by introducing a check_and_skip_if_needed. This actually fixes the root cause on fbcode and should bring some perf gain internally.
Test Plan: `buck2 test @//mode/opt //caffe2/test/dynamo:test_dynamo -- --exact 'caffe2/test/dynamo:test_dynamo - test_misc.py::DynamicShapesMiscTests::test_guards_cse_pass_single' --run-disabled`
Reviewed By: malfet
Differential Revision: D46126742
Pull Request resolved: https://github.com/pytorch/pytorch/pull/102120
Approved by: https://github.com/malfet
